The present invention relates to derivatized microfibrillar polysaccharide. More specifically, the present invention relates to microfibrillar polysaccharide stabilized by steric and/or electrostatic forces, where the electrostatic forces are provided by anionic charge, or by a combination of both anionic and cationic charge.
Polysaccharides are often found in nature in forms having fibrous morphology. Polysaccharides which are not found in nature in fibrous form can often be transformed into fibrous morphologies using fiber spinning techniques. Whether the fibrous morphology is of natural or artificial origin, the polysaccharide will often be present such that the fibers can be reduced to fibrillar and microfibrillar sub-morphologies through the application of energy.
Fibrillar and microfibrillar cellulose obtained in this manner have been considered for use in applications, including use as additives to aqueous-based systems in order to affect rheological properties, such as viscosity. The use level of these materials in aqueous systems is often on the order of about 2% by weight, below which these materials have a tendency to poorly occupy volume, and to exhibit gross inhomogeneities in distribution.
Microfibrillated cellulose and its manufacture are discussed in U.S. Pat. Nos. 4,500,546; 4,487,634; 4,483,743; 4,481,077; 4,481,076; 4,464,287; 4,452,722; 4,452,721; 4,378,381; 4,374,702; and 4,341,807, the disclosures of which are hereby incorporated by reference thereto. These documents, in part, purport to describe microfibrillated cellulose in stable, homogenous suspensions, characterized as useful in end use products including foods, cosmetics, pharmaceuticals, paints, and drilling muds.
Cellulose nanofibrils are characterized in WO 98/02486 (PCT/FR97/01290), WO 98/02487 (PCT/FR97/01291), and WO 98/02499 (PCT/FR97/01297), the disclosures of which are hereby incorporated by reference. Nanofibrils are characterized as having diameters in the range of about2 to about 10 nanometers.
EP 845495 discusses cationic cellulose particulate which is characterized as insoluble, positively charged, and used in water treatment, specifically to treat water in a paper manufacturing plant. In paper making this cationic particulate is said to remove anionic trash from the water. The particles are obtained by milling, which is stated to reduce particle size uniformly such that particles are typically round as described by a length/diameter ratio of approximately 1. Particle size is stated to be 0.001 mm (i.e., 1 xcexcm), and preferably 0.01 mm (10 xcexcm)
EP 85901 1(xe2x80x9cEP ""011xe2x80x9d) is directed to a process for obtaining cationic cellulose microfibrils or their soluble derivatives. The process is described as including making a cationic cellulose derivative and processing the derivative through a high pressure homogenizer to form transparent gels. The product can be dehydrated and rehydrated. Viscosity measurements are reported on the product at a concentration of 2% in water. EP ""011 indicates that the degree of substitution (xe2x80x9cDSxe2x80x9d) of the cellulose can range from 0.1 to 0.7, with a DS of between 0.2 and 0.7, 0.3 and 0.6, and 0.5 and 0.6 characterized as representing increasing orders of preference. The examples show cellulose with a DS ranging from a low of 0.24 up to 0.72. Gelling is reported to occur above a microfibril concentration of 10 g/L, or above 1%, in water. EP ""011 defines gelling as occurring when Gxe2x80x2 greater than Gxe2x80x3, where Gxe2x80x2 is the dynamic storage modulus and Gxe2x80x3 is the dynamic loss modulus.
Microfibrillated chitosan is reported to form uniplanar, oriented sheets upon drying by H. Yokata, J. Polymer Sci., Part C: Polymer Letters, 24:423-425 (1986). This article mentions that at a level of 4% chitosan in water, a gel is formed having a viscosity of 26,600 cps (Brookfield, 20xc2x0 C., rotor #7, 10 rpm). The microfibrillated chitosan is made by homogenization of commercial chitosan flakes in a Gaulin homogenizer. The commercial chitosan is deacetylated using sodium hydroxide.
JP 59 [1984]-84938 discusses a method for producing a chitosan suspension. Commercial chitosan separated and purified from crabs and lobsters is pulverized to pieces having maximum length of about 1-2 mm. The pieces are then suspended in water at up to 15% chitosan, and are run in multiple passes through a high pressure homogenizer at between 3,000 and 8,000 psi.
It would be desirable to obtain microfibrillar polysaccharides whose viscosity-affecting properties are achieved without the presence of cationic functionalities, at least in part because of the general lack of suitability of cationic materials for use in foods. It would also be desirable to obtain microfibrillar polysaccharides that are capable of forming a gel at concentrations of 1% or less, thereby providing economy and ease of formulation, while still providing necessary rheological behavior and homogeneity of distribution.
In addition, there is a continuing need in industry to improve the stability of commercial emulsions, such as paper sizing emulsions. At present, one method for stabilizing such emulsions is the addition of charged materials, such as cationic starches, which may be added in amounts equal to 10-20% by weight of the size component. Interaction with anionic components, such as sulfonates, can also improve stability. However, emulsion failure still takes place in such emulsions, either through density-driven separation, also referred to as creaming, or through gellation. It would accordingly be desirable to develop a material that could be added to emulsions to provide long-term stability.
The present intention is directed to derivatized microfibrillar polysaccharide, methods for its production, and applications for its use. The derivatized microfibrillar polysaccharides is derivatized to contain substituents that provide electrostatic and/or steric functionality; where electrostatic functionality is present, it includes, but is not necessarily limited to, the presence of anionic charge.
Polysaccharides suitable for use in the present invention include cellulose, hemicellulose, chitin, chitosan, guar gum, pectin, alginate, agar, xanthan, starch, amylose, amylopectin, alternan, gellan, mutan, dextran, pullulan, fructan, locust bean gum, carrageenan, glycogen, glycosaminoglycans, murein, bacterial capsular polysaccharides, and derivatives thereof. Mixtures of these may be employed. Preferred polysaccharides are cellulose, chitin, chitosan, pectin, agar, starch, carrageenan, and derivatives thereof, used singly or in combination, with cellulose being most preferred. The cellulose may be obtained from any available source, including, by way of example only, chemical pulps, mechanical pulps, thermal mechanical pulps, chemical-thermal mechanical pulps, recycled fibers, newsprint, cotton, soybean hulls, pea hulls, corn hulls, flax, hemp, jute, ramie, kenaf, manila hemp, sisal hemp, bagasse, corn, wheat, bamboo, velonia,,bacteria, algae, fungi, microcrystalline cellulose, vegetables, and fruits. Preferred sources of cellulose include purified, optionally bleached wood pulps produced from sulfite, kraft, or prehydrolyzed kraft pulping processes; purified cotton linters; fruits; and vegetables.
The derivatized microfibrillar polysaccharides that may be obtained using cellulose include, but are not limited to, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, carboxymethylcellulose, carboxymethylhydroxyethyl cellulose, hydroxypropylhydroxyethyl cellulose, methyl cellulose, methylhydroxypropyl cellulose, methylhydroxyethyl cellulose, carboxymethylmethyl cellulose, hydrophobically modified carboxymethylcellulose, hydrophobically modified hydroxyethyl cellulose, hydrophobically modified hydroxypropyl cellulose, hydrophobically modified ethylhydroxyethyl cellulose, hydrophobically modified carboxymethylhydroxyethyl cellulose, hydrophobically modified hydroxypropylhydroxyethyl cellulose, hydrophobically modified methyl cellulose, hydrophobically modified methylhydroxypropyl cellulose, hydrophobically modified methylhydroxyethyl cellulose, hydrophobically modified carboxymethylmethyl cellulose, nitrocellulose, cellulose acetate, cellulose sulfate, cellulose vinyl sulfate, cellulose phosphate, and cellulose phosphonate.
The derivatized microfibrillar cellulose of the present invention may form a gel in water throughout the concentration range of between about 0.01% and about 100%, or throughout the concentration range of between about 0.01% and about 50% in water, or at least one point in the concentration range of from about 0.05% up to about 0.99% in water. In an alternative embodiment, the derivatized microfibrillar cellulose of the present invention forms a gel in water at a concentration of about 0.95%.
The derivatized microfibrillar polysaccharide may be used in the presence of a solvent, in which it is substantially insoluble. Examples of solvents include water, alcohol, and oil.
In the case of derivatization with groups that provide electrostatic functionality, the derivatized microfibrillar polysaccharides of the present invention may have a degree of substitution of less than about 0.5, less than about 0.35, less than about 0.2, less than about 0.18, or less than about 0.1. A preferred range for the degree of substitution is between about 0.02 and about 0.5, with a range of between about 0.05 and about 0.2 being more preferred. When the derivatized microfibrillar polysaccharide is derivatized to comprise substituents that provide electrostatic functionality in the form of anionic charge, the degree of substitution representing those substituents which provide electrostatic functionality in the form of anionic charge is preferably at least about 0.05. Anionic charge may be provided, for example, by carboxyl, sulfate, sulfonate, phosphonate, or phosphate groups, or combinations thereof. Where cationic charge is also present, both charges may be provided by the same groups or substituent (i.e., the substituent may be amphoteric or zwitterionic); or, the derivatized microfibrillar polysaccharide may be derivatized to contain both substituents that contain anionic charge and substituents that contain cationic charge. In addition, the derivatized microfibrillar polysaccharides of the present invention may be obtained by blending two or more separate derivatized microfibrillar polysaccharides, where at least one has been derivatized to provide anionic charge, and at least one other has been derivatized to provide anionic charge, cationic charge, or both.
When the derivatized microfibrillar polysaccharide of the present invention is derivatized to contain substituents that provide steric functionality, the derivatized microfibrillar polysaccharides may have a molar substitution of less than about 3.0, or of less than about 1.5, or of less than about 1.0, or of less than about 0.5. The range of molar substitution may be from about 0.5 to about 3.0. Steric functionality may be provided, by way of non-limiting example, by hydroxyethyl groups, hydroxypropyl groups, methyl groups, ethyl groups; straight- or branched-chain alkyl, alkenyl, or alkynyl groups having from about 4 to about 30 carbons; and/or aryl, arylalkyl, arylalkenyl, cyclic, and heterocyclic hydrocarbons having from about 4 to about 30 carbons.
In a preferred embodiment the derivatized microfibrillar polysaccharide contains carboxymethyl cellulose, and has a degree of substitution of less than about 2.0, preferably less than about 0.35. The range of degree of substitution may be from about 0.02 to about 0.2, with a range of from about 0.10 to about 0.2 being preferred.
The derivatized microfibrillar cellulose of the present invention may form a gel at a concentration of less than about 1% in water.
In a further embodiment, the present invention is directed to a comestible composition of matter containing the derivatized microfibrillar polysaccharide of the present invention. The comestible composition of matter may, by way of non-limiting example, be a low fat, reduced fat, or fat-free food spread, such as a mayonnaise, or a salad dressing. Alternatively, the comestible composition may contain a pharmaceutically active ingredient. The derivatized microfibrillar polysaccharide may be used to provide or improve a controlled, sustained, or delayed release of a component of the comestible composition, including in particular a pharmaceutically active ingredient.
In yet another embodiment, the derivatized microfibrillar polysaccharides of the present invention may be used in non-comestible, spreadable compositions of matter, such as skin care lotions or creams, or sunscreen lotions or creams.
The present invention is further directed to a paper composition containing the derivatized microfibrillar cellulose, and particularly, though not exclusively, microfibrillar carboxymethyl cellulose.
The derivatized microfibrillar polysaccharide may be produced by using a derivatizing step to treat a microfibrillar polysaccharide to obtain the derivatized microfibrillar polysaccharide. Alternatively, a derivatized polysaccharide may be microfibrillated to produce the derivatized microfibrillar polysaccharide. In another method, the steps of microfibrillation and derivatization may take place at substantially the same time. In a preferred embodiment, cellulose is first derivatized with monochloroacetic acid or a salt thereof under alkaline conditions to produce carboxymethylcellulose; the carboxymethylcellulose is suspended in water; and the resulting suspension is homogenized to produce microfibrillated carboxymethylcellulose.
The derivatizing step may include contacting a non-microfibrillar polysaccharide with a swelling agent, such as an anionic reagent, and may take place under alkaline conditions. These alkaline conditions may include contacting the cellulose with the anionic reagent in the presence of an alkaline reagent which is sodium hydroxide, an oxide or hydroxide of an alkali metal or alkaline earth metal, an alkali silicate, an alkali aluminate, an alkali carbonate, an amine, ammonium hydroxide, tetramethyl ammonium hydroxide, or combinations thereof. The derivatization may take place at high solids.
Microfibrillation may be accomplished by applying energy to a non-microfibrillar polysaccharide under conditions sufficient to produce microfibrillar polysaccharide. The non-microfibrillar may optionally be enzyme-treated before microfibrillizing. More specifically, microfibrillation may be accomplished using homogenization, pumping, mixing, heat, steam explosion, pressurization-depressurization cycle, impact, grinding, ultrasound, microwave explosion, milling, and combinations of these. In a preferred embodiment the non-microfibrillar polysaccharide is passed through a homogenizer under conditions sufficient to produce microfibrillar cellulose; those conditions may include a pressure differential of at least about 3,000 psi, and passing the non-microfibrillar polysaccharide through the homogenizer at least three times.
The method should be conducted to yield a derivatized microfibrillar polysaccharide that is substantially insoluble in the solvent of use. Water is a preferred solvent of use, but other solvents, including but not limited to alcohols and oils, are contemplated for various applications.
The present invention extends to derivatized microfibrillar polysaccharide produced by the above methods.
In an alternative embodiment the present invention is directed to a method of modifying the rheological properties of a liquid composition of matter by incorporating the derivatized microfibrillar polysaccharides of the present invention into the liquid composition of matter.
This may be accomplished by incorporating the derivatized microfibrillar polysaccharide into a water-containing system, where it may be used, for example, to provide scale control and/or corrosion control. The rheological properties which may be modified by the derivatized microfibrillar polysaccharide include viscosity, suspension stability, gel insensitivity to temperature, shear reversible gelation, yield stress, and liquid retention.
Liquid compositions which may be Theologically modified include, as non-limiting examples, foods, pharmaceuticals, neutraceuticals, personal care products, fibers, papers, paints, coatings, and construction compositions. These include oral care products; creams or lotions for epidermal application (such as moisturizing, night, anti-age, or sunscreen creams or lotions); food spreads, including reduced fat, low fat, or fat free food spreads (such as mayonnaises); and drilling fluids.
The present invention further extends to a method of improving the physical and/or mechanical properties of a coating composition by incorporating, into the coating composition, an effective amount of the derivatized microfibrillar polysaccharide. The physical and/or mechanical properties that may be improved in this manner include film forming, leveling, sag resistance, strength, durability, dispersion, flooding, floating, and spatter.
The present invention has particular utility in the field of paper manufacture and treatment. For example, derivatized microfibrillar cellulose may be used to improve one or more of sizing, strength, scale control, drainage, dewatering, retention, clarification, formation, adsorbency, film formation, membrane formation, and polyelectrolyte complexation during paper manufacture. As a particular example, the derivatized microfibrillar cellulose may be used as a drainage aid and/or as a sizing agent. A polyelectrolyte complex containing the derivatized microfibrillar polysaccharide is also within the scope of the present invention.
Microfibrillated carboxymethylcellulose is a particularly preferred embodiment for use in paper applications. During the process of paper manufacture, the derivatized microfibrillar cellulose may be used, by way of further example, in a papermaking machine to increase the rate of drainage and/or dewatering during paper manufacture; for retention of organic and/or inorganic dispersed particles in a sheet of paper during its manufacture; to improve the uniformity of formation of a sheet of paper during its manufacture; and to improve the strength of a sheet of paper. The derivatized microfibrillar cellulose may be used in combination with any of the additives and performance enhancers conventionally used in paper manufacture, including cationic polyacrylamides; polydiallyldimethyl-ammonium chloride; cationic starch; derivatives of cellulose containing ammonium or mono-, di-, or trialkyl ammonium substituents; derivatives of guar gum containing ammonium or mono-, di-, or trialkyl ammonium substituents; resins formed by the reaction of amines and/or polyamines with epichlorohydrin; aluminum salts; hydrolyzed or partially hydrolyzed aluminum salts; complexes of hydrolyzed or partially hydrolyzed aluminum salts with organic or inorganic species; at least one polymer of ethylene oxide, ethyleneimine, allylamine, or vinylamine; and, at least one copolymer or terpolymer of ethylene oxide, ethyleneimine, allylamine, or vinylamine; and combinations thereof. In the context of retention of organic and/or inorganic dispersed particles, the particles so retained may include one or more of pulp fines, fillers, sizing agents, pigments, clays, detrimental organic particulate materials, and detrimental inorganic particulate materials.
In another embodiment, the stability of an emulsion, dispersion, or foam system may be improved by including, in the system, the derivatized microfibrillar polysaccharide of the present invention. The derivatized microfibrillar polysaccharide may be added to an existing system; added to a formulation which will be processed into such a system; or added during processing of such a formulation. Where addition takes place before completion of processing of a formulation into an emulsion, dispersion, or foam system, the processing conditions used to form the emulsion, dispersion, or foam may be used to produce the derivatized microfibrillar polysaccharide as well. Thus, a derivatized non-microfibrillated polysaccharide (where xe2x80x9cnon-microfibrillatedxe2x80x9d includes an incompletely microfibrillated polysaccharide) may be added to a formulation prior to completion of processing, and subsequent processing may then be conducted in a manner that will microfibrillate the polysaccharide. Alternatively, a microfibrillated polysaccharide may be added to the formulation, with subsequent processing conducted so as to derivatize the microfibrillated polysaccharide. In another variation, both derivatization and microfibrillation may take place during processing. Systems which may be treated in this manner include water-in-oil and oil-in-water emulsions.
The present invention also extends to emulsion, dispersion, and foam systems produced by the above methods; and, to emulsion, dispersion, or foam systems that contain the derivatized microfibrillar polysaccharide of the present invention.